Wood screw having enlarged radial pips to facilitate entry into workpiece



Nov. 8, 1960 C. H. RLACH ET AL SCREW HAVI ENLARGED RADIAL P FACILITATE ENTRY INTO WORKPIEC IPS TO E WOOD Filed Feb. 19, 1958 2 Sheets-Sheet l FIG. 2

Rotation Angular 5 INVENTORS,

CARL H. GERLACH FiGQ BY MILWDA ATTORNEY R 0 d i u s Nov. 8, 1960 GERLACH NG ENLARGED ET AL 2,959,086 RADIAL PIPS T0 2 Sheets-Sheet 2 C. WOOD SCREW HA FACILITATE ENTRY INTO WORKPIECE Filed Feb. 19, 1958 E Angu Ior Rotui i on FIG. 7

INVENTORS, CARL H. GERLACH BY MILTON F. PRAVDA ATTORNEY United States Patent WOOD SCREW HAVING ENLARGED RADIAL PIPS T0 F ACILITATE ENTRY INTO WORKPIECE Carl H. Gerlach, 36985 Pettiboue Road, and Milton F. Pravda, both of Solon, Ohio; said Pravda assignor to said Gerlach Filed Feb. 19, 1958, Ser. No. 716,100

7 Claims. (Cl. 85-46) This invention relates generally to fasteners and more particularly to a fastener which can be driven at low torque into solid wood or similar materials without splitting the material.

It is an important object of this invention to provide a fastener which can be driven into any wood in any direction relative to the grain, without a pilot or clearance hole, which will not split the wood.

' It is another important object of this invention to provide a wood screw type fastener of und-iminishing holding power which can be driven into any wood in any direction relative to the grain at virtually any proximity to the edges without producing forces which ordinarily split the wood.

It is another object of this invention to provide a crushdrilling means of making a hole or enlarging an existing hole in wood or other similar materials.

It is another important object of this invention to provide a screw which can be driven into wood incorporating means to rotationally crush back a conical recess for the head of the screw.

It is another object of this invention to provide a wood fastener which can be driven with least possible driving effort.

. It is another object of this invention to provide a screw of virtually unlimited practical length whose driving force requirements increase only slightly with screw length.

It is another object of this invention to provide a screw which produces a large easily-sensed difference in driving effort between the normal driving torque and the cinch-up torque so as to prevent inadvertent stripping of the material into which the screw is threaded.

Further objects and advantages will appear from the description and drawings, wherein:

Figure 1 is a side elevation showing a wood screw incorporating this invention;

Figure 2 is an enlarged fragmentary cross section taken along 2--2 of Figure 1;

Figure 3 is an enlarged cross section taken along 3-3 of Figure 1;

Figure 4 is an enlarged cross section taken along 4-4 of Figure 1;

Figure 5 is a graph of the machining program in terms of pitch radius versus angular rotated position of the screw;

Figure 6 is a side elevation of a second embodiment of ice countered when the force developed by the fastener in opening the hole exceeds the force necessary to split the material. Those skilled in the art will recognize that the splitting force applied to the wood is a function of the pressure of the wood along the surface of the fastener times the area of the fastener. In the past, it has been customary to drill a pilot hole so that the pressure along the fastener surface is reduced to the point where splitting will not occur or it has been necessary to use a smaller fastener. In general, even soft woods will split if the screw is large or located near the edge but in the harder types of wood such as oak, maple and the like, it is virtually impossible to drive a reasonably large standard wood screw without the use of a pilot hole to prevent splitting.

By using a fastener according to this invention, it is possible to drive a relatively large fastener into the hardest woods without producing splitting even when the fastener is driven immediately adjacent to the edge of the wood. To accomplish this non-splitting operation, we form a fastener with a small pip or projection which locally over-crushes the wood back radially just enough to form a hole of the proper size and shape to receive the main or holding portion of the thread. By confining the high crushing pressure to a relatively small area near the forward end of the fastener and thus reducing the pressure over the remaining portions, we are able to reduce the total splitting force developed to a point where splitting does not occur. Again since the forcenecessary to drive the fastener is a function of the friction along the surface of the fastener and since the friction is a function of the pressure along the surface of the fastener, reductions in the pressure over the majority of the fastener surface reduces the required driving force.

Referring now to the drawings, Figure 1 shows a fiat head wood screw incorporating this invention. This screw includes a crushing section 10 at the forward end terminating in a protrusion or pip 11 and followed by a main thread portion 12 having a pitch radius less than the maximum pitch radius occurring at the pip 11. To the right of the main thread portion 12 is the shank 13 of the screw which connects the thread portion 12 with the head portion 14. The point or crushing section 10 is formed with a relatively steep slope along which sufficient pressure is developed to crush back a hole in the wood. This slope must be low enough to permit starting of the screw in the wood but steep enough to result in a relatively small area presented to the wood in the crushing portion 10. The crushing portion terminates in a pip 11 which extends around the screw for a relatively short distance of 45 or less. Following the pip 11 is I a short ramp 16, shown in Figure 2, along which the a wood screw utilizing a plurality of crushing projections; I

Figure 7 is a machining program of the embodiment shown in Figure 6;

Figure 8 is a non-splitting nail according to this invention;

Figure 9 is a fragmentary side elevation of a drill incorporating this invention, and;

Figure 10 is a cross section Figure 9.

When driving a fastener into a material such as wood taken along 10-10 of without the use of a pilot hole, splitting is often enradius of the thread is reduced enough to reduce the unit pressure on the main portion 12 of the thread. The main portion 12 is formed of a uniform pitch radius less than the radius of the pip 11 extending to the shank 13. Because the radius of the screw is slightly reduced behind the pip 11, the unit pressure along the surface of the main thread portion 12 is reduced and forces large enough to split the wood are not developed. In other words, since the high pressure of crushing are limited to a small portion of the surface and the surface pressure is low over the remaining portions, and since the splitting forces are the product of average pressure times the area, the total force developed is much smaller than the forces developed by normal screws and splitting does not occur.

In order to enlarge the hole for the shank portion we form the second pip 17 at the forward edge of the shank portion 13. This pip should have a longitudinal length at least equal to the thread lead and a peripheral extent which is relatively short. Here again substantially all of the crushing occurs as the wood is pushed back by the leading edge of the pip 17 so the peripheral extent of the pip need not be large. The pip 17 crushes back a hole into which the shank portion 13 can move and since the shank portion 13 has a smaller radius than the radius of the pip, the pressure along the shank is relatively low.

If the screw is of the flat head type with a conical under-surface that projects into the wood, we form a plurality of pips 18 on the under side of the head portion 14 which crush out a counter-sink hole. Because the pips 18 again have a relatively short peripheral extent and since they should not extend along the screw a substantial length, it is preferable to utilize a plurality of peripherally spaced pips 18. If two pips 18 are used, their longitudinal extent should be at least one-half of a thread lead since the screw moves forward this distance in 180 of rotation. If three pips are used, they need only be approximately one-third of a lead since the forward movement of the screw is one-third of a lead in 120 of rotation. When more pips are used, shorter longitudinal extents can be used While still providing the crushing action for the counter bore to receive the head portion lid. The pip feathers down to zero longitudinal extent at the outer edge so that the crushing action becomes ineffective and thus allows desired force to build up under the head. The trailing decline or ramp section of pip 18 may be made undercut and sharp as in a barb if a means to prevent unloosening of the screw is desired.

Figure 5 is a machining program of the forward end of the thread and clearly illustrates that in this case the crushing section has a substantially constant slope extending from A to B. The pip 11 is formed of a constant radius from B to C followed by a ramp 16 reducing the radius from C to D. Actual tests have determined that the pitch radius of the pip should be greater than the pitch radius of the main portion of the screw by about 0.010 to 0.015 inch on standard type screws having diameters of approximately to A1 of an inch to achieve maximum possible splitting prevention at normal holding power. Again the height of the pip 17 should be in the same order so that the friction along the shank will be relatively low.

Referring to Figures 6 and 7, a second embodiment of this invention utilizes a plurality of pips in the crushing zone. In this embodiment, similar numerals Will be used to designate similar portions of the screw with a prime added to indicate that they refer to the second embodiment. In this case the crushing zone is formed in two or more stages which in the illustrated case is three. The advantage of this embodiment is that a sharper screw is provided that is easier to start in the wood; however, once the screw is started, each of the three successive crushing operations is the same as in the first embodiment of Figure 1. In addition, this type of screw does not split open the wood as it emerges from the far side thereof. In this case a first crushing zone 21 terminates in a first pip 22 followed by a zone of constant diameter 23 which leads to a second crushing zone and pip 24 and a second zone of a reduced radius 25. Following this portion is still the third and final pip 26. By an analysis of Figure 7, those skilled in the art will recognize that the function of each of the crushing zones and pips is the same as in the first embodiment but they have been broken up and extended axially along the screw to produce a more pointed screw which is easier to start. Normally, we form the pips so they are 540 along the screw thread from each other.

The first crushing zone 21 has a constantly increasing radius from E to F wherein it terminates in the first pip 22 having a constant radius indicated from F to G and a decreasing radius from G to H. The first zone of constant diameter 23 shown from H to I follows: The second crushing zone extends from I to J and terminates at the second pip 24 from I to K. The second zone of reduced radius 25 extends from L to M and terminates in a third crushing zone from M to N and a third and final pip 26 from N to 0. Here again a main thread portion 12' is formed with a radius indicated at P slightly less than the radius of the third and final pip 26 and the shank portion 13 is provided with a pip at 17'. If a self-countersinking fiat head screw is to be used, the head portion 14' is again provided with axial extending pips 18. Actual tests have shown that the holding power of the screw is not reduced because the threads depend upon the shear strength of the wood for the holding power.

In Figure 8 a nail is shown formed according to this invention wherein the point is formed with an annular crushing section 31 terminating at a projection or annular pip 32 of maximum radius. Immediately following the projection 32 the radius of the nail is reduced to reduce the pressure along the main shank portion 33.

In Figures 9 and 10 one form of a drill according to this invention is shown. The drill is provided with a shank 36 that can be mounted in a power or hand drill which rotates and feeds the drill into the piece being drilled. The end of the shank 36 is formed with a conical drilling portion 37 from which protrude crushing projections 38. In the illustrated embodiment the drilling portion 37 and projections 38 are symmetrical about the axis of the drill so it can be rotated in either direction. To prevent unnecessary friction the shank should have a radius less than the maximum radius of the crushing portions.

Although the preferred embodiments of this invention are illustrated, it will be realized that various modifications of the structural details may be made without departing from the mode of operation and the essence of the invention. Therefore, except insofar as they are claimed in the appended claims, structural details may be varied widely without modifying the mode of opera-' tion. Accordingly, the appended claims and not the aforesaid detailed descriptions are determinative of the scope of the invention.

We claim:

1. An elongated fastener having a helical thread extending from one end for insertion in a Wood or the like member without predrilling, said thread including a first portion extending from a point at said one end the radius of at least a root portion thereof rapidly increasing as it extends from said point and terminating in a pip of a predetermined maximum radius, said pip having a second portion of uniform maximum radius smoothly blending into said first portion, and at least a plurality of turns of thread immediately following said second portion of substantially uniform cross section concentric with said fastener, the combined circumferential extent of said pip and second portion having radii exceeding corresponding radii of said thread in said plurality of turns and being less than 2. An elongated fastener having a helical thread extending from one end for insertion in a wood or the like member without predrilling, said thread including a first portion extending from a point at said one end the radius of at least a root portion thereof rapidly increasing as it extends from said point and terminating in a pip of a predetermined maximum radius, and at least a plurality of turns of thread immediately following said second pip of substantially uniform cross section concentric with said fastener and having a corresponding radii less than said predetermined maximum radius, the surface of said pip smoothly blending from said first portion into said plurality of turns, the circumferential extent of said pip having radii exceeding corresponding radii of said thread in said plurality of turns being less than 180.

3. An elongated fastener having a helical thread extending from one end for insertion in a wood or the like member without predrilling, said thread including a first portion extending from a point at said one end the radius of at least a root portion thereof rapidly increasing as it extends from said point and terminating in a first pip of a first predetermined radius, said first pip having a second portion of uniform maximum radius smoothly blending into said first portion, said thread including a third portion immediately following said second portion of substantially uniform cross section concentric with said fastener and corresponding radii less than said first predetermined radius, a fourth portion following said third portion the radius of at least the root portion thereof increasing to a pip of second predetermined radius, a fifth portion of uniform radius smoothly blending into said fourth portion; at least a plurality of turns of thread immediately following said fifth portion having a substantially uniform cross section concentric with said fastener, the combined circumferential extent of said second pip and fifth portion have radii exceeding corresponding radii of said thread in said plurality of turns and being less than 180,

4. An elongated fastener having a helical thread extending from one end for insertion in a wood or the like member without predrilling, said thread including a first portion extending from a point at said one end the radius of at least a root portion thereof rapidly increasing as it extends from said point and terminating in a pip of a predetermined maximum radius, said pip having a second portion of uniform maximum radius smoothly blending into said first portion, at least a plurality of turns of thread immediately following said second portion of substantially uniform cross section concentric with said fastener, the combined circumferential extent of said pip and second portion having radii exceeding corresponding radii of said thread in said plurality of turns and being less than 180, a uniform radius shank on said fastener following said thread, and a second pip on the forward end of said shank having a radius greater than the radius of said shank.

5. An elongated fastener having a helical thread extending from one end for insertion in a Wood or the like member without predrilling, said thread including a first portion extending from a point at said one end the radius of at least a root portion thereof rapidly increasing as it extends from said point and terminating in a pip of a predetermined maximum radius, said pip having a second portion of uniform maximum radius smoothly blending into said first portion, at least a plurality of turns of thread immediately following said second portion of substantially uniform cross section concentric with said fastener, the combined circumferential extent of said pip and second portion having radii exceeding corresponding radii of said thread in said plurality of turns and being less than 180, a uniform radius shank on said fastener following said thread, and a second pip on the forward end of said shank having a radius greater than the radius of said shank, and a head on the other end of said fastener formed with a conical surface adjacent to said shank and a plurality of axially extending projections, the maximum axial extent of each projection being substantially equal to the thread lead divided by the number of projections.

6. An elongated fastener having a helical thread extending from one end for insertion in a Wood or the like member without predrilling, said thread including a first portion extending from a point at said one end the radius of at least a root portion thereof rapidly increasing as it extends from said point and terminating in a pip of a predetermined maximum radius, at least a plurality of turns of thread immediately following said second pip of substantially uniform cross section concentric with said fastener and having a corresponding radii less than said predetermined maximum radius, the surface of said pip smoothly blending from said first portion into said plurality of turns, the circumferential extent of said pip having radii exceeding corresponding radii of said thread in said plurality of turns being less than a uniform radius shank on said fastener following said thread, and a second pip on the forward end of said shank having a radius greater than the radius of said shank.

7. An elongated fastener having a helical thread extending from one end for insertion in a wood or the like member without predrilling, said thread including a first portion extending from a point at said one end the radius of at least a root portion thereof rapidly increasing as it extends from said point and terminating in a pip of a predetermined maximum radius, at least a plurality of turns of thread immediately following said second pip of substantially uniform cross section concentric with said fastener and having a corresponding radii less than said predetermined maximum radius, the surface of said pip smoothly blending from said first portion into said plurality of turns, the circumferential extent of said pip having radii exceeding corresponding radii of said thread in said plurality of turns being less than 180, a uniform radius shank on said fastener following said thread, and a second pip on the forward end of said shank having a radius greater than the radius of said shank, and a head on the other end of said fastener formed with a conical surface adjacent to said shank and a plurality of axially extending projections, the maximum axial extent of each projection being substantially equal to the thread lead divided by the number of pro jections.

References Cited in the file of this patent UNITED STATES PATENTS 42,475 Harvey Apr. 26, 1864 430,236 Rogers June 17, 1890 684,774 Baggs Oct. 22, 1901 1,933,332 May Oct. 31, 1933 2,070,851 Woodley Feb. 16, 1937 2,558,379 Phipard June 26, 1951 

